This invention relates to an eductor for mixing liquids, for example mixing a concentrated solution into a flow of water to provide a desired dilution of the concentrated solution. The invention also relates to a dispensing apparatus having such an eductor.
It is common practice in many industries, such as hotels and catering, for chemicals such as those used for cleaning to be purchased as concentrated liquids and then diluted with water to give the correct concentrations for use. Proportioning dispensing apparatus have been designed to achieve the desired dilution of the concentrated solution and dispense the mixed diluted solution.
These dispensers have commonly employed venturi-type devices, known as eductors, to aspirate or draw the concentrated solution into the water stream. In these eductors water travelling through a passage entrains the concentrated solution at a point where a restricted flow channel in the passage widens.
These dispensers are generally operated with water provided directly from the mains supply. In this case it is important to maintain the water supply free of contamination and thus to prevent backflow of the chemicals into the water source. In order to achieve this the eductors generally employ an air gap. Such eductors commonly have a nozzle upstream of the eductor passage, which nozzle defines a stream of water passing across an unobstructed gap in the eductor body prior to entering the passage. Some eductors also employ means to reduce splash back at the entrance to the eductor passage.
In order to ensure that the solution is dispensed at the desired concentration, a method of flow regulation is required to control the amount of concentrated solution drawn into the water flow. This has been achieved in previous eductors such as disclosed in U.S. Pat. No. 5,522,419 and WO94/04857 by means of an element having a small aperture or metering orifice in the concentrated solution feed line. This method of flow regulation has several disadvantages primarily due to the fact that the aperture is easily blocked by solid particles or deposits. This leads to problems in the accuracy and functioning of the dispensing apparatus. Such flow control devices are small elements located inside the liquid feed line and hence are difficult to remove for cleaning or changing. They are also easily damaged, during attempts to clean them.
An object of the present invention is to avoid or reduce the problems of flow restriction in eductors mentioned above. According to the invention there is provided an eductor for mixing liquids, having an eductor body containing a flow passage for a first liquid into which a dispensing passage for a second liquid opens so that in use the second liquid is drawn into the flow of the first liquid, the dispensing passage including a flow restrictor portion, wherein the flow restrictor portion is provided by a groove extending on the periphery of a restrictor plug removably received in a socket of the eductor body, the groove and the wall of the socket defining the flow restrictor portion of the dispensing passage.
This restrictor plug, having a flow-restricting groove in its periphery, is easily removed from and inserted into its position in the eductor body. It is easily manufactured to the desired accuracy and is easily cleaned, while being less liable to damage than an element having a small orifice. The plug may be arranged to be easy to insert and remove, without disturbing other portions of the flow line for the second solution, e.g. a hose connection.
Preferably the plug has a cylindrical periphery in which said groove is formed, and preferably the groove extends axially or helically along the cylindrical periphery. These are simple constructions, easy to manufacture and assemble. High precision can easily be achieved. If the plug is made by injection moulding of a plastics material, it can be avoided that xe2x80x9cflashxe2x80x9d appears at the flow-restricting groove or grooves. By contrast, when forming an aperture by injection moulding, it is difficult to avoid flash at the aperture, leading to poor accuracy or more steps in the process.
Where appropriate the restrictor plug may have a plurality of the grooves and is selectively insertable into said socket in a plurality of positions, whereby the grooves provide respectively different flow rates of the second liquid. To provide for correct positioning or indexing of the plug restrictor in the eductor body, preferably the plug and the eductor body have mutually engageable locating shapes to determine the rotational position of the plug in the socket. The locating shapes may comprise a projecting pin on the eductor body and at least one groove in the periphery of a flange of the plug.